Generac Guardian 15kW not producing power

Portable standby generator troubleshooting and repair questions. (Gasoline, diesel, propane, natural gas)
Post Reply
deni
New Member
New Member
Posts: 5
Joined: Sat Aug 03, 2019 8:18 pm

Mon Aug 05, 2019 11:44 am

Item # 0045821, serial 4177574. Was running and powering just a TV during an outage, then all of a sudden complete loss of power, followed by engine throttling down and dying. It's been sitting in the garage for a while (years) and now I'm trying to get it fixed up. Battery is long since dead so I'm hooking it up to my running car with jumper cables while doing tests. Engine starts up and runs fine but none of the outlets work. None of the 3 LEDs on the voltage regulator are lit up and the one on the bottom left PCB in the panel is also off. I measured with an AC meter and it's showing 0.17V on all outlets and frequency is ~120hz. The meter shows 110V and 60hz inside the house so it's probably not the meter. Should I test the stepper motor since the frequency is so high? Or focus on the voltage issue first?

Here is a video of it running
murphy
Contributor
Contributor
Posts: 35
Joined: Thu Nov 15, 2018 4:19 pm

Mon Aug 05, 2019 12:40 pm

The frequency is not 120. Frequency is directly proportional to RPM.
If the frequency was 120 the engine would be screaming fast at 7200 RPM and in danger of destroying itself.
Your meter can't properly read the distorted waveform of a 2 pole generator.
Only a true RMS meter can do that.

Your problem is with the alternator since the engine sounds fine to my old ears.
Take a look at the slip rings. If they are dirty the field flash to start power generation probably failed.
Chris
Site Admin
Site Admin
Posts: 918
Joined: Sat Aug 04, 2018 8:46 pm
Location: Clawson, MI
Contact:

Mon Aug 05, 2019 5:42 pm

As Murphy mentioned, the engine is running fine and sounds very close to 60Hz to me. I would start by measuring the resistance of the brushes/slip rings and see what you get. This can be done first at the AVR (wires 0 and 4). If it's normal there, no need to tear the unit apart to get to the slip rings themselves.
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
Looking for Generac parts? Gentek Power offers the full line of Generac replacement parts! Shop Gentek Power Generac Parts
A list of my favorite Generator & Electrical Tools! https://www.amazon.com/shop/gentek_power
deni
New Member
New Member
Posts: 5
Joined: Sat Aug 03, 2019 8:18 pm

Tue Aug 06, 2019 4:04 pm

Resistance is infinite at the brush terminals so that's step 1 I guess. Will pull the rotor out and go to town with 400 grit sandpaper on the brushes and rings. Or would melamine foam work as well?
Chris
Site Admin
Site Admin
Posts: 918
Joined: Sat Aug 04, 2018 8:46 pm
Location: Clawson, MI
Contact:

Wed Aug 07, 2019 9:36 am

I personally really like a XF sanding sponge! Something like this https://amzn.to/2YQm7ew

It allows it to sort of contour to the slip rings and works pretty well. I also usually take some brake clean and spray it on a rag or paper towel to first clean off the loose stuff. (DO NOT spray it directly into or onto the slip rings as it may damage the varnish)
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
Looking for Generac parts? Gentek Power offers the full line of Generac replacement parts! Shop Gentek Power Generac Parts
A list of my favorite Generator & Electrical Tools! https://www.amazon.com/shop/gentek_power
deni
New Member
New Member
Posts: 5
Joined: Sat Aug 03, 2019 8:18 pm

Wed Aug 14, 2019 11:19 am

I used some brake parts cleaner on a rag and then a bit of those XF sanding sponges. The slip rings are now nice and shiny but still have extremely high resistance (over 30 mega ohms, it jumps around). Why would slip rings have high resistance if they are clean?
Chris
Site Admin
Site Admin
Posts: 918
Joined: Sat Aug 04, 2018 8:46 pm
Location: Clawson, MI
Contact:

Wed Aug 14, 2019 3:24 pm

The resistance you're reading is not the slip rings themselves but the slip ring, through the rotor windings, then to the other slip ring. I would suggest double checking with another known good meter and if the readings are the same that rotor is trashed. It may have also wiped out the stator and AVR...

You can also check for resistance from the center metal shaft to either slip ring. You should see NO resistance readings at all, meaning completely open or OL on the meter. If you have and resistance readings from anything metal to either slip ring with the brushes still removed, the rotor also has a ground fault. (Winding insulation has failed and is touching metal)
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
Looking for Generac parts? Gentek Power offers the full line of Generac replacement parts! Shop Gentek Power Generac Parts
A list of my favorite Generator & Electrical Tools! https://www.amazon.com/shop/gentek_power
deni
New Member
New Member
Posts: 5
Joined: Sat Aug 03, 2019 8:18 pm

Wed Sep 18, 2019 6:02 pm

Ended up taking it apart with a friend and found the winding wire on the rotor broke. Soldered it back together and slip ring resistance went down to a few ohms like it's supposed to. Amazingly generator now runs and produces power! And a lesson for me about using cheap Amazon power meters.
Chris
Site Admin
Site Admin
Posts: 918
Joined: Sat Aug 04, 2018 8:46 pm
Location: Clawson, MI
Contact:

Thu Sep 19, 2019 6:03 pm

That's awesome that you were able to get it going again! Hopefully it lasts for a while.
Generac tech for over 12 years. I'm here to help!
"The only source of knowledge is experience" -Albert Einstein
Looking for Generac parts? Gentek Power offers the full line of Generac replacement parts! Shop Gentek Power Generac Parts
A list of my favorite Generator & Electrical Tools! https://www.amazon.com/shop/gentek_power
Post Reply